Abstract:

【Objective】Gliadin derived from wheat gluten has strong surface hydrophobic properties, and the gliadin colloid particles prepared by ethanol-water solution anti-solvent exhibit outstanding foaming ability and stability. However, the foam properties of gliadin under the action of heat have not been revealed yet. Therefore, in order to further promote the application of gliadin particles in real food systems, the effects of different heating temperatures and heating times on the foaming ability and stability of gliadin particles were studied in this paper. 【Method】After treating the gliadin at different temperatures (50, 70 and 90℃) for 15, 30 and 60 minutes, the gliadin particles were prepared by the anti-solvent method, and the foaming ability and foam stability were measured. By measuring the size, zeta potential, protein solubility, atomic force microscopy, infrared spectroscopy, fluorescence spectroscopy, circular dichroism, ultraviolet spectroscopy, DSC and small-angle X-ray scattering of the heat-treated wheat gliadin particles, the changing law of its surface morphology and microstructure were analyzed. 【Result】The results showed that the foaming ability and foam stability of the heat-treated wheat gliadin particles increased by 25% and 85%, respectively. With the increase of the heating temperature and the extension of the heating time, the gliadin particles had partially aggregated; the particle size increases, and it mainly distributed around 105-122 nm, and the zeta potential decreases; the degree of aggregation became greater at 90℃. The heating temperature had no obvious effect on protein solubility, but the solubility of protein has been significantly improved with the increase of heating time; the thermal effect exposed the hydrophobic amino acids inside the protein molecule, resulting in an increase in surface hydrophobicity; the content of disulfide bonds decreases, and the content of free sulfhydryl groups had no significant difference. The reason might be that the SH/SS exchange reaction of the prolamin occurs during the heating process. High temperature treatment changed the secondary structure of wheat gliadin. The fluorescence intensity of the protein at 90℃ decreased, the β-sheet content decreased, while the irregular curl content increased, and the protein was highly stretched, accompanied by partial unfolding. DSC results showed that the highest energy of wheat gliadin particles decreased from 54.33 mW to about 3 mW, the spectrum after heating was relatively flat, and the protein conformation tended to be amorphous with the extension of heating time.【Conclusion】The thermal effect caused the wheat gliadin particles to aggregate, and the exposure of the hydrophobic groups in the protein enhanced the hydrophobicity of the particle surface. Heat treatment improved the structural flexibility of the wheat gliadin (especially the 90℃ treatment), which was more conducive to the formation of stability. The interfacial film could better stabilize the foam and effectively improve the foam characteristics of the wheat gliadin colloid particles, which had outstanding practical significance for enhancing its application in the food industry.

Key words: gliadin, foamability, structural flexibility, surface hydrophobicity